Note that the NMSE between 0 (perfect estimation) and 1 (using the mean value of the variable as the estimate) measures the relative estimation error per antenna [1]}. In traditional MISO systems, a common method to reduce the NMSE is to increase the length of pilots, i.e., increasing \(\tau \) . However, Corollary REF  indicates that in RIS-aided MISO systems, increasing the number of reflecting elements of RIS can play a similar role as increasing \(\tau \) . Therefore, increasing RIS reflecting elements not only helps improve the system capacity, but also helps decrease the NMSE.
